1. Field of the Invention
The present invention relates to a method for forming a hollow article using an extrusion molding technology and an apparatus for the same, more particularly to a method for forming a hollow article using a plurality of blow molding units and an apparatus for the same.
2. Description of the Related Art
When comparatively large hollow articles such as a fuel tank for use in cars and a can are manufactured using an extrusion blow molding technology, a plurality of blow molding units, each of which comprises a blow molding mold, have been used and the receiving position where a parison is received and the position where the parison is expanded by blowing air thereinto have been made to be separate from each other. As such conventional kinds of apparatuses for the forming hollow article, the apparatus disclosed in Japanese Patent Application Laid-open No. 251441/1995, for example, has been known. The features of this apparatus are as follows.
(1) There are two or more blow molding units and there are one or more extrusion heads of an extrusion system.
(2) Each of the blow molding units is moved from a position apart in a certain direction to a detaching position of the hollow article by a first movement operation, and moved to a receiving position for receiving the parison by a second movement operation. Movement directions in the first and second movement operations are different.
(3) Each of the blow molding units is made to be an open state after it reaches the detaching position. Thereafter, the hollow article already molded in a blow molding mold is taken out, and then the blow molding mold unit is moved to the receiving position with the blow molding mold left in an open state.
However, the apparatus for forming a hollow article using the conventional extrusion molding technology has the following technological problems.
Specifically, each of the blow molding units is moved from the position apart in a certain direction to the detaching position by the first movement operation, and moved to the receiving position by a second movement operation which moves the blow molding unit to a different movement direction from the movement direction of the first movement operation. For this reason, driving devices to move the blow molding unit into the two directions are needed, so that the structure of the apparatus will be complicated and disadvantageous economically.